Road-system fire stop

ABSTRACT

A fire-resistant road-system apparatus includes at least one cover can be arranged detachably in a frame that is intended to be fixed to the ground, to close a gallery or an underground technical room to protect it from fires. A casing filled with a heat-insulating refractory material is fixed detachably under the cover. The invention is applied in road-system or railroad tunnels.

FIELD OF THE INVENTION

The present invention relates to road-system fire stop equipment comprising at least one cover or plug, which can be arranged detachably in a frame intended to be fixed to the soil, to close off a gallery or an underground technical room which has to be protected from fires.

It applies to the type of road-system equipment which is installed, for example, in road-system or railroad tunnels, and subject to drastic safety standards, requiring that the technical equipment housed in the underground rooms that are closed off by road-system equipment must be effectively protected by this equipment for a predetermined period in case of a fire in the tunnel.

BACKGROUND

Road-system equipment is known that protects the technical equipment housed in the underground room, which is closed off by the covers or plugs of the equipment, and consists in providing one or more covers comprising a heat-insulating material arranged on top of each cover, or a plug, arranged in the support frame that is secured in the ground.

This known arrangement has the drawbacks of having a very complex and consequently expensive structure, and of being difficult to install, since subcovers must be available in the technical room before closing the latter with external covers or plugs. In addition, access to the technical equipment housed in the room is not easy, because the external covers or plugs have to be removed first so that then one can reach the subcovers and remove them from the room.

SUMMARY OF THE INVENTION

The purpose of the present invention is to eliminate the above drawbacks of known fire-resistant road-system equipment.

For this purpose, the invention proposes road-system fire stop equipment comprising at least one cover or plug, which can be arranged detachably in a frame intended to be secured to the ground to close off a gallery or an underground technical room which is to be protected from fires, and characterized in that it comprises a casing that is filled with a heat-insulating refractory material and is fixed detachably under the cover.

The equipment comprises at least a second cover, which can be arranged so it rests on the frame in alignment and in the same plane as the first cover, and a second casing, which is filled with a heat-insulating refractory material and fixed detachably under the second cover.

Each cover is in the form of an inverted basin which is filled with a heat-insulating refractory material, and whose external upper wall is provided with continuous passages which are also filled with the refractory material and just come in contact with the external face of the wall of the cover.

The external upper wall of each basin of the cover is surrounded by a gutter, which is delimited by the external walls of the cover and raised parallel to perforated lateral walls of the basin opposite the walls where the refractory material fills the peripheral gutter through the holes of the lateral walls of the basin.

The external walls of each cover and the bottom wall of the peripheral gutter constitute the seat of the cover and they can come to rest with their external faces respectively on the internal faces of the lateral walls of the frame, delimiting its opening and an internal peripheral ledge integrally connected to the lateral walls of this frame.

Each cover comprises lower peripheral walls that extend under the bottom wall of the peripheral gutter to delimit the inverted basin of the cover, where these lower peripheral walls are at a separation from the lateral walls of the frame when the cover is arranged so that it rests in the frame.

It is preferred for each casing or bottom, in the form of a box containing the heat-insulating refractory material, to be fixed detachably under the corresponding cover so that the end borders of the lower walls of The basin rest on the refractory material of the casing, and the free upper parts of the walls of the casing surround, with some separation, the lower walls of the basin when the cover is arranged in its frame.

Several threaded rods are anchored by their respective heads to the wall of the corresponding cover, perpendicularly under the latter wall, opposite, respectively, continuous passages in the wall of the cover so that the heads of these threaded rods are embedded in the refractory material filling these passages, and so that the threaded rods are partially embedded in the refractory material filling the basin of the cover, protruding outside this material opposite the wall of the cover where the casing is fixed under the cover by threaded rods that traverse the refractory material of the casing, and where the lower wall forms the bottom of the casing, and is screwed by nuts to the threaded rods on the bottom wall of the casing.

The head of each threaded rod is anchored in a contact plate that is integrally connected to the internal face of the wall of the cover opposite the corresponding continuous passage of this wall.

The second cover presents a structure with an inverted basin which is filled with a heat-insulating refractory material that is substantially identical to that of the first cover, * where the external upper wall of the second cover has one of its edges, which is not bordered i by a gutter, such that it can be rest directly on the corresponding raised external wall of the first cover when the two covers are arranged in the frame, and the second cover comprises, under the border of its upper wall that rests on the external wall of the first cover, a bar arranged with clearance below the corresponding bottom wall of the gutter of the first cover, by being opposite, with some separation, the corresponding lower wall of the basin of the first cover.

According to another embodiment, each cover is in the form of a basin filled with a heat-insulating refractory material and comprises a peripheral ledge constituting the seat of the cover and delimiting the basin of the cover into two parts, an upper and a lower part, having a larger and smaller cross section, respectively, and the cover rests with its peripheral ledge on an integrally connected internal peripheral ledge of the lateral walls of the frame, so that the lateral walls of the upper part of the basin rest on the internal faces of the lateral walls of the frame, and the lateral walls of the lower part of the basin are separated from the lateral walls of the frame.

Each casing containing the heat-insulating refractory material is fixed detachably under the corresponding cover of this other embodiment, so that the bottom wall of the basin rests on the refractory material of the casing, and the free upper parts of the walls of the casing surround, with some separation, the lower part of the basin when the cover is arranged in its frame.

Several threaded rods with heads traverse the bottom wall of the basin, protruding perpendicularly under this wall, where the heads of these rods rest on the internal face of the bottom wall of the basin and are embedded in the refractory material that fills the basin, and the casing is fixed under the cover by the threaded rods that traverse the refractory material of the casing and the bottom wall of the casing, and by nuts that are screwed to the threaded rods under the bottom wall of the casing.

The second cover of this other embodiment has one of its lateral walls, which does not comprise a peripheral ledge part, present an upper part that can be placed directly on the upper part of the corresponding wall of the first cover when the two covers are arranged in the frame, and the second cover, which is integrally connected to its lateral wall, comprises a bar arranged with clearance below the corresponding ledge of the support wall of the first cover, by being opposite, with some separation, the lower part of this support wall.

Advantageously, a heat-expandable joint is interposed between the bar of the second cover and the bottom wall of the gutter of the first cover or the ledge of the first cover.

The casing with refractory material, which is fixed under the second cover identically to the casing of the first cover, extends in the same plane as the casing of the first cover, and one of its lateral walls faces, with some separation, the corresponding lateral wall of the casing of the first cover when these covers are arranged in the frame.

A part forming a joint with the heat-insulating refractory material is fixed to at least one of the bottom walls of the casings of the two covers, so that it covers the space between the two lateral walls opposite the two casings perpendicularly to this space.

Advantageously, the part forming the joint consists of a flat parallelepiped box covering the two bottom walls of the casings of the two covers, perpendicularly to the plane of the above-mentioned space, and containing the refractory material that can consist of refractory concrete, or of one or more noncombustible heat-insulating superposed plates based on calcium silicate and alumina.

The lateral walls of each cover casing are separated from the lateral walls opposite the frame, and the bottom wall of each cover casing hangs over a lower peripheral ledge of the lateral walls of the frame, where a heat-expandable peripheral joint is interposed between this ledge and the bottom wall of the casing.

Advantageously, the frame presents a modular structure with main beams and crosspieces which can be assembled detachably to each other to receive several juxtaposed covers.

The lateral walls of the frame are perforated and a heat-insulating refractory material fills the openings of these walls before embedding the frame in the ground.

The refractory material that fills the basin of each cover is, for example, concrete cast into the basin in at least two layers that can present heat and mechanical resistance properties that differ from one layer to the other, and the material filling the openings of the main beam and crosspieces of the frame is also concrete cast into these openings.

The material that fills each cover casing consists of concrete or one or more heat-insulating noncombustible superposed plates based on calcium silicate and alumina.

The continuous passages are in the form of oblong holes distributed over the main portion of the surface of the upper wall of each cover.

Each cover is rectangular in shape.

Each casing can be replaced by another casing having a different height from that of the preceding one, and can be fixed detachably under the corresponding cover being filled with a heat-insulating refractory material.

BRIEF DESCRIPTION OF DRAWING FIGURES

The invention will be understood better, and other purposes, characteristics, details and advantages of the invention will become clearer in the following explanatory description, which is made in reference to the drawings in the appendix that are given only as an example illustrating two embodiments of the invention, in which drawings:

FIG. 1 is a lower half-view with transverse cross section of a railroad tunnel comprising several road-system equipment items in accordance with the invention;

FIG. 2 is a perspective view from above of the road-system equipment of the invention with two covers arranged in a frame and filled with concrete;

FIG. 3 is a perspective view similar to that of FIG. 2 with one of the covers removed from the frame, and the other cover empty;

FIG. 4 is a perspective view of a modular assembly with main beams and crosspieces of the frame of the road-system equipment of the invention;

FIG. 5 is a perspective view from below of one of the covers of the equipment of FIGS. 2 and 3;

FIG. 6 is an enlarged view of the circled part at VI of FIG. 5;

FIG. 7 is a view of the cover of FIG. 5 filled with a refractory material;

FIG. 8 is a perspective view of one of the covers of FIG. 2;

FIG. 9 is a partial perspective view from below of the junction between the two adjacent covers of FIG. 2;

FIG. 10 is an enlarged cross-sectional view along line X-X of FIG. 2;

FIG. 11 is a perspective view of a casing fixed under one of the covers of the road-system equipment of FIG. 2;

FIG. 12 is a cross-sectional view along line XII-XII of FIG. 2; and

FIG. 13 is a cross-sectional view along line XIII-XIII of FIG. 2;

FIG. 14 is a perspective view from above of road-system equipment according to a second embodiment, and comprising two covers arranged in a frame;

FIG. 15 is a perspective view similar to that of FIG. 14 with one of the covers removed from the frame, and the other cover empty;

FIG. 16 is a view from below of a cover filled with concrete according to this second embodiment;

FIG. 17 is a view from above of a cover of the second embodiment, which is not filled with concrete;

FIG. 18 is a cross-sectional view along line XVIII-XVIII of FIG. 14;

FIG. 19 is an enlarged view of the circled part at XIX of FIG. 18;

FIG. 20 is an enlarged cross-sectional view along line XX-XX of FIG. 14; and

FIG. 21 is a an enlarged cross-sectional view along line XXI-XXI of FIG. 14.

DETAILED DESCRIPTION

FIG. 1 represents two road-system equipment items 1 of the invention, which can be installed in a railway tunnel T to close a technical room or gallery 2 in which technical installations are housed, such as, for example, electrical cables C.

Each road-system equipment item 1 is capable of protecting, for a predetermined duration, the electrical installations in the technical gallery or room 2 from a considerable increase in the external temperature due to a fire propagating in the tunnel T.

The road-system equipment of the invention which is resistant to fire or acts as a fire stop will now be described in reference to FIGS. 2-13, for the case where this equipment comprises two rectangular covers or plugs 3, 4, which are arranged detachably in a frame 5, in alignment and in the same plane, although it must be clearly understood that this equipment can be of the type comprising a single circular, triangular or rectangular cover or a plug, which can be housed in a frame, or several rectangular, or triangular plugs housed in the corresponding frame.

The cover plug 3 has the general shape of an inverted basin whose external upper flat wall 6 is provided with a large number of continuous passages 7, preferably in the form of oblong holes, occupying the majority of the surface of the rectangular wall 6 of the cover 3.

The upper wall 6 of the cover 3 is surrounded completely by a gutter 8, which is delimited by raised external walls 9 of the cover 3 which are parallel to the perforated walls 1O of the basin of this cover.

The frame 5 consists of a modular assembly of main beams I 1 and crosspieces 12, which can be assembled to each other to define the four peripheral lateral walls 13 of the rectangular frame 5. As is more apparent from FIG. 4, two main beams 11 on the same side are assembled end to end by two external flat lugs 14, which extend perpendicularly to the corresponding main beams and are held together, in juxtaposition, by at least one bolt, not shown, traversing its lugs. This figure also shows that each crosspiece 12 is fixed at each end of a main beam by means of two flat lugs 14, which are integrally connected perpendicular to the corresponding main beam 11, and to the end of the crosspiece 12, respectively, in its extension, so that the two lugs 14 can be fixed to each other by being held together, in juxtaposition, by at least one traversing bolt, not shown. Thus, this modular structure makes it possible to extend, in alignment with each other, other main beams 11 with the help of external lugs 14, depending on the number of covers one wishes to arrange in the frame 5.

The external walls 9 of the cover 3 and the bottom wall 15 of the peripheral gutter 8 constituting the seat of this cover have external faces resting, respectively, on the internal faces of the lateral walls 13 of the frame 5 and an internal peripheral ledge 16 made of the same material as the walls 13 of the frame 5.

The cover 3 comprises four lower peripheral walls 17, which extend under the bottom wall 15 of the peripheral gutter 8 to delimit the inverted basin of the cover 3. As is apparent notably from FIG. 13, the lower peripheral walls 17 are at some distance from the lateral wall parts 13 of the frame 5, which are located below the bottom wall 15 of the gutter 8.

The basin of the cover 3 is completely filled with a heat-insulating refractory material, consisting preferably of Concrete BF cast into the basin of the cover 3, which is represented in its inverted position in FIG. 5, so that the concrete not only fills this basin, but also the continuous passages 7 of the upper wall 6 of the cover 3, coming just in contact with the external face of this wall as well as the peripheral gutter 8 by passing through holes 10 a of the lateral walls 10 of the basin of the cover 3. This filling with refractory material considerably decreases the thermal bridges between the cover 3 and the technical room 2. Only the four passages 7 located at the four corners of the cover 3 are not filled with concrete and are used only for introducing a tool for lifting the cover 3 during an intervention in the technical room.

FIG. 7 shows the refractory concrete BF completely filling the basin of the cover 3 of FIG. 5, so that the concrete is just in contact with the peripheral margins of the lower walls 17 of this cover.

It is preferred for two layers of refractory concrete to be cast successively into the cover 3, where these two layers can have different fire and mechanical resistance properties. Thus, the first layer of refractory concrete cast on the lower face of the plate 6 of the cover 3 can have a higher mechanical resistance than the second underlying layer, and a lower fire resistance and/or lower heat insulation than the second layer.

Before casting the refractory concrete into the inverted cover 3, a certain number of threaded rods 18, in the present case four, are anchored by their respective heads 19 in plates 20, so that the heads 19 are, respectively, opposite certain continuous passages 7 with the rods protruding from the lower face of the wall 10 of the cover 3 perpendicularly to this face. By casting the concrete into the inverted cover 3, the concrete introduces itself particularly into the continuous passages 7 opposite the screw heads 19 to embed them in concrete and thus cut off any thermal bridge that may be created by the threaded rods 18. Once the inverted basin 3 has been completely filled with the refractory Concrete HF, the end parts of the threaded rods 18 project from the concrete layer opposite the wall 6 of the cover 3.

A casing 21 in the form of a box with rectangular cross section, more clearly visible in FIG. 11, which contains a heat-insulating refractory material, is fixed under the cover 3, so that the end edges of the lower walls 17 of the basin of this cover rest on the refractory material of the casing 21. The refractory material does not completely fill the casing 21, so that it leaves free the upper parts of the walls 22 of the casing, which surround, in a spaced manner, and along a space e1, the lower walls 17 of the basin of the cover 3, when the casing 21 is fixed under this cover, as can be seen notably in FIG. 12. The casing 21, which contains the refractory material, is fixed under the cover 3 by the threaded rods 18 that traverse the refractory material BF of the casing and the corresponding perforations 23 provided in the bottom wall 24 of the casing 21, and by nuts 25 screwed to the free ends of the threaded rods 18 resting on the external face of the bottom wall 24.

The refractory material contained in the casing 21 can consist of refractory Concrete BF, or one or more layers of heat-insulating noncombustible plates based on calcium silicate and alumina, which in themselves are known.

The lateral walls 22 of the casing 21 are arranged opposite the lower parts of the lateral walls 13 of the frame 5, defining between themselves a space e2, and the bottom wall 24 of the casing 21 protrudes over a lower peripheral ledge 13 a of the walls 13 of the frame 5 extending perpendicularly to these walls leaving a space e3 between this ledge and the wall 24, in which a joint J1 made of a heat-expandable material can be housed.

The walls 13 of the main beams 11 and crosspieces 12 of the frame 5 comprise openings in the form of windows 26, which are filled with a refractory material, preferably refractory concrete, before the frame is embedded in the ground.

The second cover 4 of the road-system equipment 1 presents the general structure of an inverted basin filled with a refractory material, which is substantially identical to the structure of the first cover, so that the elements of the cover 4 that are identical to those of the cover 3 bear the same reference numerals and are not described again.

The difference between the cover 4 and the cover 3 concerns the fact that the upper wall 6 of the cover 4 is only bordered by the gutter 8 on three of its sides, and the free edge of the fourth side of the wall 6 rests directly on the adjacent raised external wall 9 of the cover 3, and the cover 4 comprises, on this edge resting on the adjacent wall 9 of the cover 3, a bar 27 extending transversely between the main beams 11 of the frame 5, engaging under the bottom wall 15 of the gutter 8 located below the adjacent wall 9 of the cover 3, and forming a clearance e4 between the upper face of the bar 27 and the lower face of the wall 15 of the gutter. A heat-expandable joint J2 can be housed in the space e4. In addition, the bar 27 is arranged opposite, with some separation, the adjacent lower wall 17 of the basin of the cover 3. This assembly makes it possible to produce a fire stop baffle.

A casing 21, identical to the casing 21 of the cover 3, is fixed under the cover 4 in the same manner as the casing 21 of the cover 3 with the help of sets of threaded rods 18 that traverse the refractory material contained in the casing 21 of the cover 4 and with nuts 25 that are screwed to the free ends of these threaded rods.

The two casings 21 extend adjacently in the same plane with two of their lateral walls 22 adjacent to each other, and separated by a space e5.

A relatively flat parallelepiped box 28, filled with a heat-insulating refractory material, such as, for example, concrete or one or more heat-insulating noncombustible superposed layers based on calcium silicate and alumina, is arranged in part on the external faces of the two bottom walls 24 of the adjacent casings 21, by covering, perpendicularly to the walls, the space e5 of the adjacent walls 22 of the casings 21, so as to increase the properties of fire resistance and/or heat insulation of the road-system equipment.

It is preferred for the casing 28 to be fixed, for example, by welding, in part to the wall 24 of one of the casings 21, for example, the one that is fixed under the cover 4, where said wall extends perpendicularly to the wall 22 of the casing 21 and protrudes below this wall to rest directly under the bottom wall 24 of the other casing 21 when the cover 4 is arranged in the frame 5 engaging under the cover 3. Thus the casing 28 extends perpendicularly to the plane of the space e5.

FIGS. 14-21 represent another embodiment of the fire stop road-system equipment of the invention.

According to this embodiment, the elements of the road-system equipment that present the same structure and fulfill the same functions as those of the first embodiment described above bear the same reference numerals and are not described in detail again; only the elements of the second embodiment that are different from those of the first embodiment will be described below.

Thus, each of the covers 3, 4 of the road-system equipment consists of a basin that is right side up and comprises a peripheral ledge 15 constituting the seat of the cover and delimiting the basin of this cover into two peripheral parts, an upper 9 a and lower 9 b peripheral part, which have larger and smaller transverse cross sections, respectively, where the lower part 9 b of the peripheral walls 9 of the basin of the cover 3, 4 is connected to the bottom wall 9 c of the basin. The cover 3, 4 rests with its peripheral ledge 15 on the internal peripheral ledge 16 of the lateral walls 13 of the frame 5, so that the lateral walls 9 of the upper part 9 a of the basin rest on the internal faces of the lateral walls 13 of this frame, and the lower part 9 b of the lateral walls 9 of the basin are at some distance from the lateral walls 13 of the frame 5, as one can see more clearly in FIG. 21.

Each basin of the covers 3, 4 is completely filled with a heat-insulating refractory material, such as concrete B, in such a manner that they embed the plates 29, for example, four such plates, as represented in FIG. 5, which protrude from the internal face of the bottom wall 9 c of the basin and whose upper ends comprise oblong holes 29 c for introducing a tool or key for lifting the cover 3, 4 from its frame 5, where the refractory material BF is cast into the basin to come just in contact with the ends of the plates 29.

The bottom wall 9 c of the basin of each cover 3, 4 comprises perforations, for example, four perforations, for the passage of the threaded rods 18, whose heads 19 rest on the internal face of the bottom wall 9 c in such a manner that the threaded rods project from the bottom wall 9 c, perpendicularly to the latter. The threaded rods 18 are held so that they are integrally connected to the cover 3, 4 by the refractory material embedding the heads 19 of these rods in the basin.

As can be seen more clearly in FIG. 19, all the threaded rods 18, heads 19 and nuts 25 make it possible to detachably fix the casing 21 under the corresponding cover 3, 4, so that the bottom wall 9 c of the basin of this cover rests on the heat-insulating refractory material, such as concrete, which fills the casing 21. In addition, the lateral walls 22 of this casing are separated by their upper parts from the lower part 9 b of the peripheral walls 9 of the cover 3, 4, along a peripheral space e1, thus cutting off any thermal bridge. As represented in FIG. 20, the cover 4 has one of its lateral walls 9 not comprising a ledge 15, but a bar 27 integrally connected exterior to this lateral wall 9 and engaging below the ledge 15 of the other cover 3, along an area e4 when these two covers 3, 4 are arranged in the frame 5 in side-by-side opposition closing the latter. In this position, the upper part 9 a of the wall 9 of the cover 4 rests on the upper part 9 a of the lateral wall 9 of the cover.

The road-system equipment of the invention constitutes an adaptable modular set that effectively resists fire while being also mechanically resistant, and it is easy to handle in practice like a conventional cover to gain access to the technical installations housed in the underlying gallery or technical room.

The road-system equipment is arranged in such a manner that it eliminates almost all the thermal bridges that can conduct heat into the underground room. As a nonlimiting example, the road-system equipment is capable of maintaining the internal temperature of the room 2 at a value below 100° C. for two hours while the external temperature is approximately 1100° C.

The road-system equipment of the invention is adaptable, that is, its fire stop performances can be improved by replacing the lower casing of the cover with another casing having a greater height, so that it can be filled with a greater thickness of heat-insulating refractory material without changing the cover. 

1. A fire stop road-system apparatus comprising: a first cover which can be arranged detachably in a frame intended to be fixed to the ground, to close a gallery or an underground technical room to protect it from fires, wherein the first cover is filled with a heat-insulating material, and a casing filled with a heat-insulating refractory material fixed detachably under the first cover.
 2. The apparatus according to claim 1, comprising a second cover filled with a heat-insulating refractory material, and which can be arranged to rest in the frame aligned and co-planar with the first cover, and a second casing filled with a heat-insulating refractory material fixed detachably under the second cover.
 3. The apparatus according to claim 2, wherein each of the first and second casings is fixed detachably under the respective first and second covers through threaded rods traversing the refractory material and bottom walls of the first and second casings, and nuts engaging the threaded rods at the bottom walls of the first and second casings, and the threaded rods have heads that are embedded in the refractory material of the first and second covers.
 4. The apparatus according to claim 2, wherein each of the first and second covers has an inverted basin shape, is filled with a heat-insulating refractory material, and has an external upper wall with continuous passages which are filled with the refractory material in contact with external faces of the upper walls of the first and second covers.
 5. The apparatus according to claim 4, wherein the external upper wall of the basin of each of the first and second covers is surrounded by a gutter defined by raised external walls parallel to perforated lateral walls of the basin opposite the raised external walls, and the refractory material fills the peripheral gutter through holes of the perforated lateral walls of the basin.
 6. The apparatus according to claim 5, wherein the external walls of each of the first and second covers and a bottom wall of the peripheral gutter constitute a seat of the first and second covers for resting with external faces, respectively, on internal faces of lateral walls of the frame and an internal peripheral ledge integrally connected to the lateral walls of the frame.
 7. The apparatus according to claim 6, wherein each of the first and second covers comprises lower peripheral walls that extend under the bottom wall of the peripheral gutter defining the inverted basin shape of the first and second covers, the lower peripheral walls are spaced from the lateral walls of the frame when the resting in the frame.
 8. The apparatus according to claim 7, wherein each casing containing the heat-insulating refractory material is fixed detachably under the respective cover so that end edges of the lower walls of the basin shape rest on the refractory material of the casing, and free upper parts of walls of the casing surround, and are spaced from, lower walls of the basin shape when the covers are in the frame.
 9. The apparatus according to claim 3, wherein the threaded rods are anchored with heads against the wall of the respective cover, perpendicularly under the wall, opposite, respectively, continuous passages of the walls of the first and second covers, so that the heads of the threaded rods are embedded in the refractory material filling these passages, and the threaded rods are partially embedded in the refractory material filling the basin shape of the first and second covers, and protruding opposite the wall of the first and second covers.
 10. The apparatus according to claim 9, wherein the head of each threaded rod is anchored in a plate integrally connected to an internal face of the wall of the first cover, opposite the corresponding continuous passage of the wall.
 11. The apparatus according to claim 2, wherein the second cover includes an inverted basin filled with a heat-insulating refractory material, which is substantially identical to that of the first cover, the external upper wall of the second cover, at an edge which is not bordered by a gutter, can rest directly on a corresponding raised external wall of the first cover when the first and second covers are arranged in the frame, and the second cover comprises, under the edge of an upper wall that rests on the external wall of the first cover, a bar arranged with clearance below the wall of the corresponding bottom wall of the gutter of the first cover by being opposite, and spaced from, the corresponding lower wall of the basin of the first cover.
 12. The apparatus according to claim 5, wherein each of the first and second covers has a basin shape, which is filled with a heat-insulating refractory material and comprises a peripheral ledge constituting a seat of the cover and dividing the basin shape of the cover into two parts, an upper part and a lower part, having larger and smaller sections, respectively, and the first and second covers rest with the peripheral ledge on the internal peripheral ledge, which is integrally connected to the lateral walls of the frame, so that the lateral walls of the upper part of the basin shape rest on the internal faces of the lateral walls of the frame, and the lateral walls of the lower part of the basin shape are spaced from the lateral walls of the frame.
 13. The apparatus according to claim 12, wherein each casing containing the heat-insulating refractory material is fixed detachably under the respective cover in such a manner that the bottom wall of the basin shape rests on the refractory material of the casing, and the free upper parts of the walls of the casing surround, and are spaced from, the lower part of the basin when the first and second covers are arranged in the frame.
 14. The apparatus according to claim 12, wherein the threaded rods have heads transverse to the bottom wall of the basin shape, protruding perpendicularly under the bottom wall, and the heads rest on an internal face of the bottom wall of the basin and are embedded in the refractory material that fills the basin shape.
 15. The apparatus according to claim 12, wherein the second cover, at one of the lateral walls which does not comprise the peripheral ledge, has an upper part that can rest directly on the upper part of the corresponding wall of the first cover when the first and second covers are arranged in the frame, and the second cover comprises, as an integral part of a lateral wall, a bar, which is arranged with a clearance below the corresponding ledge of the support wall of the first cover and opposite, and spaced from, the lower part of the support wall.
 16. The apparatus according to claim 15, including a heat-expandable joint interposed between the bar of the second cover and the bottom wall of the gutter of the first cover, or the ledge of the first cover.
 17. The apparatus according to claim 13, wherein the casing with refractory material, which is fixed under the second cover identically to the casing of the first cover, extends in the same plane as the casing of the first cover, and has a lateral wall opposite, and spaced from, the corresponding lateral wall of the casing of the first cover when the first and second covers are arranged in the frame.
 18. The apparatus according to claim 17, comprising a part, which forms a joint with heat-insulating refractory material, fixed to at least one of the bottom walls of the casings of the first and second covers and covering a space between two opposite lateral walls of the two casings.
 19. The apparatus according to claim 18, wherein the part that forms a joint consists of a flat parallelepiped box covering the bottom walls of the casings of the covers, perpendicularly to the space and containing the refractory material consisting of refractory concrete or at least one heat-insulating noncombustible superposed plate based on calcium silicate and alumina.
 20. The apparatus according to claim 13, wherein the lateral walls of each casing of the first and second covers are spaced from opposite lateral walls of the frame, and the bottom wall of each casing protrudes over a lower peripheral ledge of the lateral walls of the frame, and including a heat-expandable peripheral joint is interposed between the lower peripheral ledge and the bottom wall of the casing.
 21. The apparatus according to of claim 2, wherein the frame a modular structure of main beams and crosspieces that can be assembled detachably to each other to receive the first and second covers.
 22. The apparatus according to claim 21, wherein the lateral walls of the frame are perforated, and a heat-insulating refractory material fills the holes of the lateral walls before embedding the frame in the ground.
 23. The apparatus according to claim 22, wherein the refractory material that fills the basin shape of each of the first and second covers is concrete that has been cast into the basin shape in at least two layers, which present different heat and mechanical resistance properties, and the material that fills the holes of the main beams and crosspieces of the frame is concrete cast into the holes.
 24. The apparatus according to claim 2, wherein the material that fills each cover casing consists of concrete or at least one heat-insulating, noncombustible superposed plate based on calcium silicate and alumina.
 25. The apparatus according to claim 4, wherein the continuous passages are oblong holes distributed over the upper walls of each of the first and second covers.
 26. The apparatus according to claim 2, wherein each of the first and second covers has a rectangular shape.
 27. The apparatus according to claim 1, wherein each casing can be replaced by another casing having a different height from that of the preceding one and fixed detachably under the respective cover and filled with a heat-insulating refractory material. 